Principle equations which contain field equations for particles of all spins and helicities are proposed. In particular, from Poincare Casimir invariants field equations for massive Klein-Gordon, Dirac, vector and Rarita-Schwinger fields were obtained. The same approach was applied to massless particles. In that case the Weinberg idea that Lorentz invariance induces local gauge transformations is confirmed. As is well known Wigner define a particles as irreducible representation of Poincare group. But, as Weinberg showed irreducible representations for vector field with helicity $\pm 1$ do not exist. Namely, Lorentz transformation of some physically relevant fields like vector field, have additional term in the form of gauge transformations. So, for these fields we can obtain actions as gauge invariant expressions of eigenvectors. In particular we can obtain Maxwell equations and Einstein equation in weak field approximation. As a consequences, Wigner's definition of particles as irreducible representations of Poincare group, which valid in massive case, in massless case must have an improvement. We can define physical massless fields as a class of equivalence, where two fields are equivalent if they relate by gauge transformation. The action is expression which depend on class of equivalence. This approach can be widely used to construct field theory for systems in various fields of physics. The only input parameter is symmetry group of the system, so that all theories with same symmetry group will look the same at sufficiently low energy.